An aptamer agonist of the insulin receptor acts as a positive or negative allosteric modulator, depending on its concentration

Abstract

Aptamers are widely used as binders that interact with targets with high affinity or as inhibitors of the function of target molecules. However, they have also been used to modulate target protein function, which they achieve by activating the target or stabilizing its conformation. Here, we report a unique aptamer modulator of the insulin receptor (IR), IR-A62. Alone, IR-A62 acts as a biased agonist that preferentially induces Y1150 monophosphorylation of IR. However, when administered alongside insulin, IR-A62 shows variable binding cooperativity depending on the ligand concentration. At low concentrations, IR-A62 acts as a positive allosteric modulator (PAM) agonist that enhances insulin binding, but at high concentrations, it acts as a negative allosteric modulator (NAM) agonist that competes with insulin for IR. Moreover, the concentration of insulin affects the binding of IR-A62 to IR. Finally, the subcutaneous administration of IR-A62 to diabetic mice reduces blood glucose levels with a longer-lasting effect than insulin administration. These findings imply that aptamers can elicit various responses from receptors beyond those of a simple agonist or inhibitor. We expect further studies of IR-A62 to help reveal the mechanism of IR activation and greatly expand the range of therapeutic applications of aptamers.

Functional selectivity of insulin receptor revealed by aptamer-trapped receptor structures

“…The A62 aptamer not only acts as an agonist, but also positively regulates the binding of insulin to IR at low concentrations 18 . The structure of the IR A62+Ins complex is asymmetric, with one insulin and one A62 bound at each site of the dimer (Fig.…”

“…These ligands include antibodies, peptides, and nucleotides that selectively activate the AKT pathway and induce metabolic effects, but exert much weaker MAPK pathway signaling and mitogenic effects than insulin 13 – 17 . Moreover, some IR agonists also lead to site-specific mono-phosphorylation of Tyr1150 (m-pY1150) in the kinase domain of IR 17 , 18 . Thus, studies of these agonists of suggest that the early IR intermediates with site-specific Tyr phosphorylation in the activation event are responsible for the selective stimulation of the metabolic signaling 17 .…”

“…Previously, we developed two DNA aptamers with modified bases that modulate autophosphorylation and downstream signaling of IR. IR-A62 (A62) is an aptamer agonist for IR that preferentially induces m-pY1150 in the kinase domain and selectively stimulates the AKT pathway and glucose uptake 18 . The IR-A43 aptamer (A43) is a positive allosteric modulator that enhances IR activation by stabilizing insulin binding 30 .…”

The Insulin Receptor: An Important Target for the Development of Novel Medicines and Pesticides

“…They can specifically and strongly bind to the target with high affinity due to their unique 3D structures [ 151 ]. Studies have reported on various aptamers ( Table 2 ), such as IR-A48 [ 152 ], IR-A43 [ 153 ], IR-A62 [ 154 ], and GL56 [ 155 ]. IR-A48 is an agonistic aptamer that binds to and then activates the IR [ 152 ].…”

“…IR-A43 is a sensitizing aptamer that effectively binds to the IR and enhances insulin sensitivity [ 153 , 156 ]. IR-A62 acts as a biased agonist that binds to the extracellular domain of the IR and preferentially induces Y1150 monophosphorylation of IR [ 154 ].…”